A Luer nut is a device that is usually used in the medical field to hold two liquid carrying fittings together. The fittings have a Luer taper as described in the American National Standard ANSI/HIMA MD70.1-1983. The Luer taper is used to make quick, leak proof connections, and is comprised of two tapered pieces, one male and one female. The male and female parts are drawn together to make a tightly fitting connection. The connection is held together by a male thread on the female Luer taper part and a nut-like device with internal threads, called a Luer nut, on the male Luer taper part.
An improved Luer nut is disclosed by Thomas P. Stephens in U.S. patent application, Ser. No. 740,353, entitled "Non-Loosening Luer Nut", filed June 3, 1985. The internal cross section of the threaded section of the improved Luer nut is not round like previous Luer nuts, but is generally in the shape of a polygon that is deformable rather than stiff. The polygonal cross-section of the improved Luer nut frequently is in the general shape of a triangle with rounded sides each with a relatively large average radius and rounded corners each with a relatively small radius, which is referred to as a trilobate shape.
Unfortunately, the plastic molding of such a Luer nut having a polygonal internal cross-section is a significant problem. In general, prior molding techniques for conventional plastic nuts utilize a mold cavity with fixed dimensions to define the outside shape of the nut, and a removable, externally threaded core within the mold cavity around which the plastic nut is molded. After the plastic is injected into the mold cavity and allowed to solidify, the threaded core is simply unscrewed, and the finished nut ejected along a parting line of the mold. Such a technique will generally not work for a nut which is not internally round in section, because the threaded core for the polyognal Luer nut must also be polygonal in external cross section. Such a non-round threaded core cannot generally be unscrewed from within the solidified nut without damaging the sides of the nut due to the fixed dimensions of the mold cavity.
One solution to this problem is to extract the polygonal core from within the cavity while the nut is still attached. Then, a secondary apparatus acting like a human hand can be used to grab and hold the outside of the nut at points adjacent to the vertices of the polygonal section, so that the core can be unscrewed without stripping the threads. Naturally, such a procedure is time consuming and expensive.
A second solution to the problem of molding such a polygonal nut is to use a collapsible core. That is, the threaded core is designed so that it can be folded in on itself after the plastic has solidified. Unfortunately, Luer nuts are generally small, with an internal diameter on the order of five millimeters. In general, building a collapsible core with such small dimensions is impractical.